A union is things coming together, or uniting, to make one. When the thirteen colonies that became the United States came together, they formed a union. Marriage is another kind of union.

Workers come together to form trade unions so that together they can have a stronger voice negotiating with their employer. The word famously occurs in the Preamble (the introduction) to the United States Constitution: "We the people of the United States, in Order to form a more perfect ordain and establish this Constitution...." You may recognize the Latin root unum in union, as in e pluribus unum "from many, one," the motto on the seal of the United States.

Definitions of union
  1. noun
    the state of being joined or united or linked
    “there is strength in union
    synonyms: unification
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    the state of lacking unity
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    coalition, fusion
    the state of being combined into one body
    connectedness, connection, link
    the state of being connected
    colligation, conjugation, conjunction, junction
    the state of being joined together
    the state of being connected together as in memory or imagination
    a close and intimate union
    the union (or attempted fusion) of different systems of thought or belief (especially in religion or philosophy)
    anastomosis, inosculation
    a natural or surgical joining of parts or branches of tubular structures so as to make or become continuous
    the junction between two neurons (axon-to-dendrite) or between a neuron and a muscle
    alliance, confederation
    the state of being allied or confederated
    federalisation, federalization
    the state of being under federal control
    the state or condition of touching or of being in immediate proximity
    the state of being linked together as in a chain; union in a linked series
    interconnectedness, interconnection
    a state of being connected reciprocally
    coherence, coherency, cohesion, cohesiveness
    the state of cohering or sticking together
    type of:
    the way something is with respect to its main attributes
  2. noun
    the act of making or becoming a single unit
    “the union of opposing factions”
    synonyms: conjugation, jointure, unification, uniting
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    the termination or destruction of union
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    coalescence, coalescency, coalition, concretion, conglutination
    the union of diverse things into one body or form or group; the growing together of parts
    reunification, reunion
    the act of coming together again
    tribalisation, tribalization
    the act of making tribal; unification on a tribal basis
    having the function of uniting a group of similar things
    an annual school or university reunion for graduates
    type of:
    combination, combining, compounding
    the act of combining things to form a new whole
  3. noun
    the occurrence of a uniting of separate parts
    “lightning produced an unusual union of the metals”
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    union of sperm and egg in sexual reproduction
    fusion, merger, unification
    an occurrence that involves the production of a union
    combine, combining
    an occurrence that results in things being united
    (genetics) a combining of genes or characters different from what they were in the parents
    (physics) a combining of charges or transfer of electrons in a gas that results in the neutralization of ions; important for ions arising from the passage of high-energy particles
    combining into a solid mass
    mix, mixture
    an event that combines things in a mixture
    conglobation, conglomeration
    an occurrence combining miscellaneous things into a (more or less) rounded mass
    type of:
    happening, natural event, occurrence, occurrent
    an event that happens
  4. noun
    a set containing all and only the members of two or more given sets
    “let C be the union of the sets A and B”
    synonyms: join, sum
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    direct sum
    a union of two disjoint sets in which every element is the sum of an element from each of the disjoint sets
    type of:
    a group of things of the same kind that belong together and are so used
  5. noun
    a political unit formed from previously independent people or organizations
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    confederacy, confederation, federation
    a union of political organizations
    the union of Greece and Cyprus (which is the goal of a group of Greek Cypriots)
    an association of states or organizations or individuals for common action
    customs union
    an association of nations to promote free trade within the union and set common tariffs for nations that are not members
    a federation of tribes (especially Native American tribes)
    Creek Confederacy
    a North American Indian confederacy organized by the Muskogee that dominated the southeastern part of the United States before being removed to Oklahoma
    Hanseatic League
    a commercial and defensive confederation of free cities in northern Germany and surrounding areas; formed in 1241 and most influential in the 14th century when it included over 100 towns and functioned as an independent political power; the last official assembly was held in 1669
    Five Nations, Iroquois League, League of Iroquois, Six Nations
    a league of Iroquois tribes including originally the Mohawk, Oneida, Onondaga, Cayuga and Seneca (the Five Nations); after 1722 they were joined by the Tuscarora (the Six Nations)
    a customs union comprising Belgium and Netherlands and Luxembourg
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    political entity, political unit
    a unit with political responsibilities
  6. noun
    an organization of employees formed to bargain with the employer
    “you have to join the union in order to get a job”
    synonyms: brotherhood, labor union, trade union, trades union
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    industrial union, vertical union
    a labor union that admits all workers in a given industry irrespective of their craft
    craft union
    a labor union whose membership is restricted to workers in a particular craft
    company union
    a union of workers for a single company; a union not affiliated with a larger union
    I.W.W., IWW, Industrial Workers of the World
    a former international labor union and radical labor movement in the United States; founded in Chicago in 1905 and dedicated to the overthrow of capitalism; its membership declined after World War I
    Teamsters Union
    an industrial union of truck drivers and chauffeurs and warehouse workers
    United Mine Workers, United Mine Workers of America
    an industrial union of mine workers in North America
    type of:
    organisation, organization
    a group of people who work together
  7. adjective
    of trade unions
    “the union movement”
    union negotiations”
    “a union-shop clause in the contract”
    requiring union membership
    organised, organized, unionised, unionized
    being a member of or formed into a labor union
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    not belonging to or not allowing affiliation with a trade union
    not requiring union membership
    nonunionised, nonunionized, unorganised, unorganized
    not affiliated in a trade union
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  8. noun
    the state of being a married couple voluntarily joined for life (or until divorce)
    “God bless this union
    synonyms: marriage, matrimony, spousal relationship, wedlock
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    having two spouses at the same time
    common-law marriage
    a marriage relationship created by agreement and cohabitation rather than by ceremony
    endogamy, inmarriage, intermarriage
    marriage within one's own tribe or group as required by custom or law
    exogamy, intermarriage
    marriage to a person belonging to a tribe or group other than your own as required by custom or law
    marriage of convenience
    a marriage for expediency rather than love
    an unsuitable alliance (especially with regard to marriage)
    the state of having only one husband at a time
    monogamousness, monogamy
    having only one spouse at a time
    open marriage
    a marriage in which each partner is free to enter into extraneous sexual relationships without guilt or jealousy from the other
    the state of a husband whose wife has committed adultery
    having more than one spouse at a time
    a Shiite tradition of temporary marriage permitted in Iran that allows a couple to specify the terms of their relationship; can last from a few minutes to 99 years
    a marriage with a person of inferior social status
    having only one wife at a time
    serial monogamy
    a succession of short monogamous relationships (as by someone who undergoes multiple divorces)
    having more than one husband at a time
    having more than one wife at a time
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    marital status
    the condition of being married or unmarried
  9. noun
    the act of pairing a male and female for reproductive purposes
    synonyms: conjugation, coupling, mating, pairing, sexual union
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    assortative mating
    mating of individuals having more traits in common than likely in random mating
    disassortative mating
    mating of individuals having traits more dissimilar than likely in random mating
    cross, crossbreeding, crossing, hybridisation, hybridization, hybridizing, interbreeding
    (genetics) the act of mixing different species or varieties of animals or plants and thus to produce hybrids
    the act of mating closely related individuals
    service, servicing
    the act of mating by male animals
    dihybrid cross
    hybridization using two traits with two alleles each
    monohybrid cross
    hybridization using a single trait with two alleles (as in Mendel's experiments with garden peas)
    reciprocal, reciprocal cross
    hybridization involving a pair of crosses that reverse the sexes associated with each genotype
    test-cross, testcross
    a cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait so the unknown genotype can be determined from that of the offspring
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    sex, sex activity, sexual activity, sexual practice
    activities associated with sexual intercourse
  10. noun
    healing process involving the growing together of the edges of a wound or the growing together of broken bones
    synonyms: conglutination
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    the natural process by which the body repairs itself
  11. noun
    a device on a national flag emblematic of the union of two or more sovereignties (typically in the upper inner corner)
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    an emblematic design (especially in heraldry)
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